diff --git a/csharp/src/Google.Protobuf.Test/ByteStringTest.cs b/csharp/src/Google.Protobuf.Test/ByteStringTest.cs
index 0ef8d8f4e798..adbbc3ef5470 100644
--- a/csharp/src/Google.Protobuf.Test/ByteStringTest.cs
+++ b/csharp/src/Google.Protobuf.Test/ByteStringTest.cs
@@ -110,6 +110,18 @@ public void CopyFromByteArrayCopiesContents()
             Assert.AreEqual(10, bs[0]);
         }
 
+        [Test]
+        public void CopyFromReadOnlySpanCopiesContents()
+        {
+            byte[] data = new byte[1];
+            data[0] = 10;
+            ReadOnlySpan<byte> byteSpan = data;
+            var bs = ByteString.CopyFrom(byteSpan);
+            Assert.AreEqual(10, bs[0]);
+            data[0] = 5;
+            Assert.AreEqual(10, bs[0]);
+        }
+
         [Test]
         public void ToByteArrayCopiesContents()
         {
diff --git a/csharp/src/Google.Protobuf/ByteString.cs b/csharp/src/Google.Protobuf/ByteString.cs
index 74dc865e9d43..e7d5f4dc83f2 100644
--- a/csharp/src/Google.Protobuf/ByteString.cs
+++ b/csharp/src/Google.Protobuf/ByteString.cs
@@ -245,6 +245,7 @@ public static ByteString CopyFrom(byte[] bytes, int offset, int count)
         /// are copied, so further modifications to the span will not
         /// be reflected in the returned <see cref="ByteString" />.
         /// </summary>
+        [SecuritySafeCritical]
         public static ByteString CopyFrom(ReadOnlySpan<byte> bytes)
         {
             return new ByteString(bytes.ToArray());